[chbot] Cheap, low voltage, high current h-bridge

[Andrew McDougall]

Hi Hanno
 
If you want CHEAP then I have used discrete BJT's. 
The BC807/BC817 will run 400mA and cost 0.02NZD each
If you can up the voltage and down the current you get a cheap H-Bridge
with low loss
 
6 BC807/817's = 0.12
4 BAS16 diodes = 0.08
6 0805 resistors = 0.042
parts cost = 0.242
 
the downside is you don't get heaps of current and SMT is the cheapest
(NZ not china) way to assemble.
If you need a bit more current the BC807 will parallel with some
derating. 
 
 
Andrew

	-----Original Message-----
	From: chchrobotics-bounces at lists.linuxnut.co.nz
[mailto:chchrobotics-bounces at lists.linuxnut.co.nz] On Behalf Of Hanno
Sander
	Sent: Friday, 14 March 2008 4:23 p.m.
	To: Christchurch Robotics
	Subject: [chbot] Cheap, low voltage, high current h-bridge
	
	
	Hi,
	I'm looking for a:
	- cheap (ideally <$5 with less than 5 parts)
	- low voltage (battery powered, so 6-8Volt)
	- high current (nominal ~500mA, but spikes to 1 or 2 Amps)
	H-bridge to drive a geared "rc car" motor.  
	
	This must be a common problem for hobbyists, but I can't find a
discrete component that fits the bill.  I've tried L293 and L298 which
are cheap, ok on current, but terrible for low voltage- since they eat 2
Volts- which also heats them up over time.
	
	I'm reasonably happy with the LMD18200T, but at $14, it's not
cheap, and with a minimum voltage of 12 volts, it doesn't do low
voltage.
	
	Mass-manufactured items, like toy robots, seem to make their own
h-bridges using FET's - is that the solution?
	Hanno
	
	

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