# Adding Darlington transistor in parallele to increase current does not work

I have a circuit that must provide PWM to a motor which is expansive in current (around 1.2 A for 4.5V). For the moment I use 100% duty, but I cannot reach the same efficiency as the one I get when I plug the motor directly on the batteries (3x1.5V = 4.5V).

The circuit I used firstly is this one :

+12V ---------+---------+
|         |
/ \        |
|M| motor ---  1N4001
\ /       / \
|         |
+---------+
|
|/
CTL -/\/\/--|    2N2222 NPN
1k    |\>
|
---
-


but then I cannot reach enough voltage so I made a Darlington transistor :

and I replaced the transistor of the first picture by this one. But the current was still under what I wanted (around 0.6A while I want 1.2A), so I tried to put two Darlington transistors in parallel :

+12V ---------+---------+
|         |
/ \        |
|M| motor ---  1N4001
\ /       / \
|         |
+---------+-----------+
|                     |
|/                    |/
CTL -/\/\/--|         CTL -/\/\/--|    <-- Darlington
1k    |\>             1k    |\>
|                     |
---                   ---
-                     -


(each "transistor" here is made with two 2N2222A transistors)

But the current stays at around 0.3-0.6A... Why the current isn't added to provide me 1.2A, but stays at the same level as before ? Is their any other way to proceed to reach 1.2A with 2N2222A transistors ?

Thank you in advance.

• First, you're going to have continuous frustration trying to distribute the current between multiple 2n2222 transistors for this amount of load. You are partially on the right track to use a darlington arrangement, but not with this transistor as the main driver. Second, if ever there was a good time to make the jump to using a power MOSFET design, this is it. Only a MOSFET will maximize the power to your motor circuit. And if for some reason your control voltage is too small to control the MOSFET gate, you can always use a transistor there. – Randy Jan 12 '17 at 1:12
• Use the first circuit, get a transistor with a higher Hfe. Darlingtons are on the right track. – Bradman175 Jan 12 '17 at 3:51
• increase the mechanical load on the motor. – Jasen Jan 12 '17 at 6:30
• @Randy : The only MOSFET I have is the IRFZ44N, but the result are not really better... Are 3.3V in input, and 4.5V for the motor enough? – tobiasBora Jan 12 '17 at 10:13
• @Bradman175: Do you have any good model of transistor ? I'm a bit lost in all the options. – tobiasBora Jan 12 '17 at 10:13