Apart from all the other mistakes, you can not use a peltier to heat to 100C.
It will melt/break at around 80C.
You need another solution.

 

Yes. Thanks. I forgot that point.

 

The L298 bridge will only carry 2A max.
The TEC12706 operates at up to 6A.

You could use a MOSFET bridge.
Below is the LTspice simulation of a simple bridge circuit that should work.
One input generates current in one direction through the TEC and the other input in the other direction.

The N and P MOSFETs can be any rated at ≥20V Vds and ≤25mΩ on-resistance.
The N-MOSFETs must be logic level type devices.

V2 and V3 are the Raspberry's outputs.

Note that you must make sure V2 and V3 are never on at the same time or you will short the bridge.

View attachment 130459

Hi, Thanks crustchow. One doubt regarding your simulation. why you connecting the load terminal to gate of the mosfet?

 

The L298 bridge will only carry 2A max.
The TEC12706 operates at up to 6A.

You could use a MOSFET bridge.
Below is the LTspice simulation of a simple bridge circuit that should work.
One input generates current in one direction through the TEC and the other input in the other direction.

The N and P MOSFETs can be any rated at ≥20V Vds and ≤25mΩ on-resistance.
The N-MOSFETs must be logic level type devices.

V2 and V3 are the Raspberry's outputs.

Note that you must make sure V2 and V3 are never on at the same time or you will short the bridge.

View attachment 130459

Thanks. Understood it well enough

 

why you connecting the load terminal to gate of the mosfet?

When one of the bottom N-MOSFETs is turned on, its drain voltage goes to ground.
This turns on the opposite P-MOSFET to complete the circuit through the load.

 

Thanks crutshow. Based on your information, I understood some stuffs and built a H-bridge circuit using 2 PNP (TIP127) and 2 NPN (TIP122G) transistor.

Now i am testing it in the breadboard. Load I connected is peltier TEC12706. I gave power supply 6V as input. But the peltier is not providing any heating. and also in simulation I have to get 3A current across the load with respect to 50% duty cycle. can you help me why this circuit is not providing proper output?

 

You bridge has some fatal errors.

First, you need resistors in the base of all the transistors to limit the current.
Each base-emitter junction looks like a forward-biased diode with about 0.7V drop.
The resistors should be selected to limit the base current to about 1/10th of the collector current.

Second, the PNP top transistor on one side has to have a low base signal while the bottom NPN transistor on the other side has to have a high signal for the bridge to conduct proper current into the load.
The other PNP transistor must have a high base signal (6V) and the bottom NPN base must be grounded so they are off.
You can do that by driving both transistors on the same side (through their respective base resistors) from the same 0-6V signal.

But note that configuration will have some transistor feedthrough current when switching which my cross-coupled technique avoids.

 

Note:
Most breadboards are not designed to handle currents as high as 3A.

 

You bridge has some fatal errors.

First, you need resistors in the base of all the transistors to limit the current.
Each base-emitter junction looks like a forward-biased diode with about 0.7V drop.
The resistors should be selected to limit the base current to about 1/10th of the collector current.

Second, the PNP top transistor on one side has to have a low base signal while the bottom NPN transistor on the other side has to have a high signal for the bridge to conduct proper current into the load.
The other PNP transistor must have a high base signal (6V) and the bottom NPN base must be grounded so they are off.
You can do that by driving both transistors on the same side (through their respective base resistors) from the same 0-6V signal.

But note that configuration will have some transistor feedthrough current when switching which my cross-coupled technique avoids.

Yes. you are correct. I modified it.

View attachment 131143

Simulation is working but when I connected the same circuit in breadboard ,the voltage is not properly going across the peltier.
Peltier is heating well and cooling mode is not working as per the reverse current. Is this due to the breadboard fault as Alec_t said in previous post

 

Is this due to the breadboard fault

It's not a breadboard fault. It's a breadboard-user fault .

 

It's not a breadboard fault. It's a breadboard-user fault .

Ok cool. i don't think i am making mistake in the breadboard connection. That's y asked.

Thinking the power(5v/6V) is not enough to drive the peltier

 

Have you read post #21?
Why are you using a TEC for heating?

 

Have you read post #21?
Why are you using a TEC for heating?

we are planning to heat one aluminium block which will be placing on top of the TEC12706.

Why? This TEC is not a best option?

It will go till 80deg celsius know?

 

we are planning to heat one aluminium block which will be placing on top of the TEC12706.

Why? This TEC is not a best option?

Use heating element.

It will go till 80deg celsius know?

I don't know.
How big is the aluminium block?

 

Use heating element.


I don't know.
How big is the aluminium block?

Its just a 6cm*5cm. Small block only. That's y we are going ahead with TEC

 

Simulation is working but when I connected the same circuit in breadboard ,the voltage is not properly going across the peltier.

Because the circuit still not correct.

You added base resistors for the bottom transistors, why not the top ones?

Also the saturation voltage of those transistors is about 2V each

so the voltage across the TEC will be about 4V less than the supply voltage.
Each ON transistor will thus dissipate about 6W @ 3A.
(You really should learn how to read data sheets).

I suggest you to use some appropriate MOSFETs instead.
They must be logic-level types.

 

Its just a 6cm*5cm. Small block only. That's y we are going ahead with TEC

Why don't you try it and see what happens?
Forget the PWM. Power the TEC directly from a DC power supply.
Start off with 6VDC and increase to 12VDC and then 15VDC.

Are you prepared for a destroyed TEC?

A TEC is a heat pump and only about 50% efficient. That is, you put it twice as much power to move the required power.
A heating element would be better.

 

Because the circuit still not correct.

You added base resistors for the bottom transistors, why not the top ones?

Also the saturation voltage of those transistors is about 2V each
View attachment 131151
so the voltage across the TEC will be about 4V less than the supply voltage.
Each ON transistor will thus dissipate about 6W @ 3A.
(You really should learn how to read data sheets).

I suggest you to use some appropriate MOSFETs instead.
They must be logic-level types.

Hey crustchow.

Thanks. I am not a well experienced person. Last year i completed my BE degree.
I am just started learning electronics stuff and making small circuits and testing everything in real scenario.
I don't have any guide to correct my mistake. Thats why posting questions.

I know my questions will be easier and sometimes innocent also in your perspective. since this is my starting stage, I am not
feeling unconfortable to ask silly questions.

Anyway i will learn to read the datasheet.

Thanks for all your post. After adding base resistor at the top of the pnp, my breadboard circut is working, peltier is heating and cooling.

Because of you, i solved the problems.

Thanks for your advise