We don't know what you're using to drive your existing H-bridge.

Why don't you post a schematic of what you have now?

 

I just make it up by using the H bridge and control by input H or L by transitor. There is no drawing on my simple circuit.

Thanks,
kevin

 

Is your input to the MOSFETs 5V Logic, or 12V? What current ability does the driving signal have?

 

There has to be drawing, you need to have something to look at when designing, troubleshooting and setting up a pcb. No matter how simple the circuit, a schematic or wiring diagram is always helpful.

 

Here is the circuit. Please review. I am using 5V for input and 12VDC for Motor.

Thanks,
Kevin

 

Are you using PWM for speed control or just switching the motor on and off at full speed in different directions?

 

Actually PWM is the switching on and off of the drive to the motor in a given direction.

hgmjr

 

Actually PWM is the switching on and off of the drive to the motor in a given direction.

hgmjr

That's what I was referring to, I was asking if the control was performing speed and direction manipulation or just direction alone.

 

No, I don't need speed control. I just need drirection forward and revert

Thanks,
Kevin

 

That diag doesnt look right, The gate drives are set up for a dead short when activated. For one direction Q2 & Q3 should be on, to reverse Q1 & Q4 should be on !!

 

That diag doesnt look right, The gate drives are set up for a dead short when activated. For one direction Q2 & Q3 should be on, to reverse Q1 & Q4 should be on !!

Glad someone else brought this up. I'm a beginner and thought it was just my way of thinking. Couldn't figure out why no one else saw that, so just kept quiet. As drawn the schematic shows all mosfets on when ever 12 V power is on.

 

Can soemone explain what is PWM? How to protect burn from my diagram circuit?

 

PWM = Pulse Width Modulation. It's usually performed at frequencies > 100Hz. A transistor or MOSFET is switched ON for a period of time, and then turned OFF for another period of time. It's much more efficient than using linear regulation.

If you want to keep it simple and stay with P-ch MOSFETs for the high side, you should choose a lower Vdss rating P-ch MOSFET with a higher Id rating. The N-ch MOSFETs I recommended earlier would work well for the low side.

 

ok, Thanks, SgtWookie. I will searching the P-channel.

 

This is an old post, but I could not help notice that people need some help designing H-Bridge circuits. I have designed quite a few low, medium, and high power DC-to-DC converters and always try and follow the KISS principle.

Those stating that the use of a lower RDS-ON N-Channel MOSFET should be used are absolutely CORRECT! Try using FETs with an ON-Resistance on the order of milliohms...the IRF3804S-7P by IR has a ultra-low 1.6milliohm ON-Resistance. IF you are driving a 2A motor with the 0.6ohm FET, switching to this lower RDS-ON FET will reduce your power dissipation (heat) from ~0.72W to just ~5.12microWatts! (That is 0.00000512W!). Your devices will stay cool and you will benefit by having a higher efficiency driver (note: MORE POWER at the Output!).

There are several appropriate drivers that can be used, the HIP4081A by Intersil isa nice one. They incorporate Boot-Strap circuitry to bias the gates of the upper N-Channel FETs to turn them on. They vary, but a typical POWER MOSFET requires a Vgs (gate to source voltage) of 3V-12V to turn it completely on. These drivers do that for you. Many of them also contain internal logic to prevent both FETs on one side of the bridge from simultaneously turning on...failure to account for this releases that magic smoke that makes all integrated circuits operate.

Even if you do NOT need speed control, the IC driven bridge is still a great starting point. they will provide ample current to drive the gates of the FETs quickly which further reduces the power dissipation of the circuit. Just remember that larger FETs have higher gate charges...this requires more current to turn it on as fast as a smaller FET.

N-Channel devices are produced with lower RDS-ON values than P-Channel devices of the same size. Just make sure that the Vds (Drain to Source voltage) rating of the FETs is ~2X the maximum supply voltage to the bridge. Verify that the IC-driver uses internal clamping to prevent the gate drives from exceeding ~15V...they typically have an internal zener that does this. Failure to clamp this gate voltage could result in permanent damage to the FET and will likely destory the bridge.

Noise can be very critical in H-Bridge designs. Crosstalk between signals can cause a gate to be driven high accientally thus shorting out one side of the bridge. Keeping the gate drive leads as short as possible is key. Running the gate drive lines directly over (opposite side of PCB) will reduce noise emmisions and ringing from the miller effect. Generally, a High side FET is kept on while the opposite Low side FET is PWM'ed for speed control. Keep the driver close to the low side FETs to minimize the gate trace length. Consider adding ~10-ohm series gate resistors between the drivers and the FET gates to slow the rise and fall times which reduces EMI and ringing.

Verify that you have designed in a dead-time delay between changing directions. The FETs turning off must COMPLETELY turn off before turning on the other FETs or you will have a short and the magic smoke will be let out. The HIP4081A lets you set the delay time using (2) external resistors.

What else...oh yeah...you will want to switch at speeds > 15kHz to avoid an annoying audible tone from your bridge. Switching at speeds below this is OK for some, but you are now within the human ear's range and will create music. Make sure you provide a decent amount of capacitance around the bridge from the positive supply to ground. Use a low ESR cap rated for 2-3X the maximum supply voltage. You should size it such that it has enough capacitance to keep the supply ripple <5% when operating under heavy load. You may have a more strict requirement for ripple with your design...please verify with an oscillioscope.

Make sure you size the traces on the board correctly...use an online trace width calculator and be conservative. Also make sure you have good solid connections everywhere...they are the root of 99% of all failures. Seriously. The part from the MFG was not bad...you misconnected it or you have a weak connection somewhere. Be very cautious to ever point the finger at the chip/IC manufacturer...it is probably just you and your design causing problems.

Just remember that all ICs have tiny little Dr. Seuss-like mechanical machines inside with micro-turbines that operate on pressurized smoke. If you ever let this smoke out, the part will cease to work. Plus it smells bad.

Make sure you have fun!

 

...pressurized smoke.

I knew the device was pressurized, but not the smoke! Well, that answers 40 years worth of questions!

joe

 

... Plus it smells bad.

Make sure you have fun!

I actually like the smell.