ULN2003+TIP32 Driving Relays

[thunderdog]

Hi,
I have "cut-and-paste" a working circuit to save some time. Please see the attachment for details. The circuit seems to be designed to use the ULN2003 to drive several TIP32 PNP transistors, which in turn drive several relays. The pins named "uP Pin" are connected to various I/O pins on the microcontroller. My problem is that I can't seem to get an output (locations Out1, Out2, Out3). At most, I get about 1.5volts. The only part of the circuit that seems to be working is the one driving the 2N4402 xistor. The output (J20) does toggle between the 12V and gnd. Can anyone explain a bit better what's going on here or why I can't seem to get the proper outputs ?
Thanks.

 

[bobcat1]

HI

The ULN2003 is an open collector device - you need to add a base resistor from ULN2003 output pin to VCC

All the best

Bobi

The microcontroller specialist

 

[pranam77]

The said circuit will work fine when a "HI" logic is fed to the inputs. Mean to the points where "uP Pin" is mentioned. This circuit will work well with a PIC micro as the pins are capable of providing a "HI" logic directly by programming. In case you are using an Atmel Micro, you need to pull up the said pins through 10K resistors and then Pull down the same through the micro pin....Thus the atmel micro pin floats if the relay is to be enrgised....Cheers

 

[karesz]

Hi thunderdog,
Did you controlled "TIP32-1 Base" too?
K.

 

[FvM]

Did you controlled "TIP32-1 Base" too?

Good point. The first prerequisite for successful "copy and paste" is to to understand the circuit somehow.

 

[Tahmid]

The said circuit will work fine when a "HI" logic is fed to the inputs. Mean to the points where "uP Pin" is mentioned. This circuit will work well with a PIC micro as the pins are capable of providing a "HI" logic directly by programming. In case you are using an Atmel Micro, you need to pull up the said pins through 10K resistors and then Pull down the same through the micro pin....Thus the atmel micro pin floats if the relay is to be enrgised....Cheers

Hi pranam77,
I didn't quite get what you said about the Atmel micro. Care to explain?
Thanks.
Tahmid.

 

[thunderdog]

After "exercising" the circuit a bit more, here is the situation. BTW. I am using a Freescale HCS08 microcontroller, which can souce 10mA. I don't believe driving the ULN2003 should be a problem.
When I give "TIP32-1-BASE" a logic high from the uP, I do get 12V at the Q4 collector. However, if I drive any other pin high (uP Pin into the ULN2003), Q4's collector voltage drops to 1.7V (which would be the same voltage at the emitters of Q1, Q2 and Q3. As I mentioned, driving the ULN inut pin labelled "2N4402-B" will toggle the collector of Q5 properly (with the 2N4402 transistor) between 12V and gnd. It seems that driving the base low of either Q1,Q2 or Q3 to about 2.4V (one diode drop higher than the base of Q1,Q2orQ3) has the effect of pulling that node down from 12V to 1.7V.
I have 12V on the ULN2003 COM pin and supply the microcontroller with 5V.
Thanks.

 

[karesz]

Hali,
What are the varistors for a Ohmic value pls?
K.

Added after 25 minutes:

You see, I think that your circuit need some load to connect into the out jacks...
Than if your varistors are low ohms, their on situation is a short, or low Ohmic value at the Q4-" Collector Bus", and clear makes a small voltages on their -or are you other meaning pls?
K.

 

[thunderdog]

Thanks for the input Karesz. The varistors are: V22ZA1P. From the datasheet:

Varistor Voltage at 1mA DC test current: Vnom=18.7; Vnom_max=26
Maximum Clamping Voltage: Vc:43, Ipk=2.5

The voltage at the varistor can be anywhere from 12V to 15V, so I'm not sure what the actual ohmic value is. I would have thought it would be pretty high since 18.7V/1mA produces a pretty high resistance.

I do have some additional results to report: After re-reading the ucontroller datasheet, it seems that most of the I/O for this device is multiplexed with LCD drivers. On reset, I/O is open-collector. I tried putting a 10K pull-up resistor on the I/O going into the ULN2003, and the circuit is now working (I think). However, the TIP32 transistors are getting very hot even though no-load is applied. I am wondering if the varistors are causing the low impedance path. The voltage on the TIP32 collectors can go as high as 15V, so even though the Vnom of the varistors is 18.8V, I may be getting a fairly low impedance path at that voltage. The circuit is supposed to work at 12V at the collector, so I'll look for a supply putting out the 12V. I'm not sure if putting a load on the outputs would change things since it would be in parallel with the varistors.