Hello,
I am pretty new to electronics. I want to design an H-bridge so I may switch a Linear Actuator On/Off and reverse the polarity using a microcontroller. The Motor/Linear Actuator is rated at 12V, 5A on load. The Microcontroller can generate 5V and a Maximum of 40mA to switch the circuit. How many inputs would I require from the Microcontroller? What kind of transistors and with what power ratings should I use?
Thanks
-Falven

 

Hi, for FFW and REV operations, you can implement with only 2 I/O, for the transistors I would use TIP 1XX, MOSFET should have smallers foot print, use a fast flyback diode across power transistor (some transistor have one in already) do a google search I've got tons of hits. Pick one and if you have anymore questions, come back here.

 

Put H bridge in find box, this page, upper right. Consider Sgt Wookie's two SPDT relay H-bridge, assuming actuator has limit switches. http://forum.allaboutcircuits.com/attachment.php?attachmentid=17722&d=1269657559

 

Put H bridge in find box, this page, upper right. Consider Sgt Wookie's two SPDT relay H-bridge, assuming actuator has limit switches. http://forum.allaboutcircuits.com/attachment.php?attachmentid=17722&d=1269657559

There are no SPDT Relays that can handle the power specifications I mentioned. What I am confused about is the schematic I would need and the power ratings for the Transistors.
So I can just buy 4 Mosfetts (What power specs?) and set them up in this configuration, no diodes, resistors or anything and it will work reliably? What would be the duty cycle? Keep in mind I have never designed or built an H Bridge or anything similar really before so detailed help would be really appreciated.
-Falven

 

There are no SPDT Relays that can handle the power specifications I mentioned.
-Falven

What do you mean by this? Are you referring to your 40mA max uC output?

 

What do you mean by this? Are you referring to your 40mA max uC output?

No, what I mean by this is that there are no DPDT relays with a contact rating of 5A and a coild voltage of 12V that can be switched by my 40mA Microcontroller outputs.
I believe a solid-state H-Bridge is my best option, but there are no IC's that can handle my power secifications either, so I need ot build one form scratch.
My qeustion still stands...
Thanks for the help thus far,
-Falven

 

You can use a transistor as driver for your relay. This is very simple to do. This is mentioned in the forum Ebook Volume 3. http://www.allaboutcircuits.com/vol_3/index.html
However I think the topic is better explained here
http://www.electronics-tutorials.ws/transistor/tran_4.html

 

I didn't imply that you should drive relays directly from your uC. That's what driver transistors are for. Here's a basic discrete BJT H-Bridge controlled by a uC.

Here's a link to a marathon thread on the H-Bridge design. It includes some common pitfalls that are sometimes encountered.

http://forum.allaboutcircuits.com/showthread.php?t=47688

 

Here is the circuit I designed.
I need a second opinion, will this work?

Here is the list of parts:
4 FDP6030BL Mosfets
2 IR21844 drivers.
Vcc - capacitor .1 Ufd. ceramic
IN - 40 mA PWM Microcontroller output.
Dt - resistor 47K
R gate - (from the outputs to the FET gates) 33 ohms
Diode - 1N5817 Vss to your micro ground.
Cap from the diode to Com .1 Ufd. ceramic
Cap Vb to Vs .047 Ufd ceramic.

 

All your Mosfets are upside down. They are N-channel so the drain connects to positive voltages. Look at the correct schematic in the datasheet for the Mosfet driver IC.

 

Put H bridge in find box, this page, upper right. Consider Sgt Wookie's two SPDT relay H-bridge, assuming actuator has limit switches. http://forum.allaboutcircuits.com/attachment.php?attachmentid=17722&d=1269657559

Ha, I actually designed this same H Bridge using relays without ever having looked at Wookie's post. Its a very easy design, and very simple and cheap. But its probably not power efficient. I have used it before though and successfully.