The DC-DC converter and A/C (air-con) motor driver…


sits underneath the power electronics that drive the two motor/generators in a gen 2 (2004-2009) Toyota Prius.  It uses the 200V battery to drive the air conditioning system compressor and also to generate a 12V rail to charge the car battery and run stuff like lights and speakers (and all the computers n stuff).

What it looks like inside:



The DC-DC converter is a “forward converter.”  It uses an h-bridge of IGBTs to chop 200VDC into the primary of a step-down transformer.  The output of the secondary is rectified and filtered to make a nice clean 12-14VDC.

The relevant circuit diagram (shown below) was found in the most informative and excellent Hybrid Vehicle Control Manual.


How Turn On???

tl;dr these two connectors


want this


and these ring terminals want 200VDC.  Observe polarity!


Setup Details

Here is my prius battery simulator.  It is a variac into a bridge rectifier into a couple of capacitors.


here is my 12V “car battery.”  It is grounded to the inverter housing

IMG_1680 IMG_1681

Here is +12V connected to the necessary pins and “before” shot of voltage on the 12V battery.

IMG_1683 IMG_1684

After switching on the variac, the 12V battery voltage jumps up.

IMG_1685 IMG_1686

and the DC clamp meter says we’re charging at half an amp.


We’re pulling about 90mA from the 200V rail.


The converter works down to about 140VDC.  The 12V output sags from 14V down to about 12.5V when dropping the input from 200V to 140V.  I didn’t test overvoltage on the input.  We’ll leave that the impending vehicle integration…