- We haven't heard from Bram Van Zoelen for a long time but he would be happy
to see how his Z-bridge has evolved.
The Z-bridge is ideal for a microcore since it is smokeless even if the
microcore saturates. Typically pin 2 and 3 go to Nv1 and Nv3 (Motor 1
reverse/forward) and pin 14 and 13 go to Nv2 and Nv4 (motor 2
reverse/forward). The enable pins 1 and 15 go to the PNC Nu output pin
The original "direct drive" Z-bridge used a 74S139 or 74F139 to drive a
motor without an additional h-bridge. We can now use the cheaper and more
efficient 74AC139 for direct drive. Stack'm for more current.
The z-bridge is also used to make the Tilden h-bridge smokeless.
Pin 5 and 6 connect to one h-bridge input resistors and pin 11 and 10
connect to the second h-bridge input resistors.
Since the decoded 139 output pins can never be simultaneously active low the
h-bridge is protected from illegal input conditions.
In a microcore controlled two motor walker using z-bridge protected
h-bridges, reversing is accomplished by adding a circuit to swap the Nv2 and
Nv4 connections to the Z-bridge. The Nv2 and Nv4 outputs of the microcore
control rear motor M2 and swapping the Nv outputs changes the order of the
motor rotations and causes the walker to back up.
One mutation of the Z-bridge is the reversable Z-bridge shown in the
attached. It avoids the additional reversing chip by using all four decoded
outputs and four h-bridge input resistors cleverly summed together to drive
the h-bridge. The diode and 1M resistor form a simple OR gate for the Enable
line pin 15. If Nv2 or Nv4 is low the 139 is enabled. The A input (pin 14)
connects to Nv4 and determines if the even or odd decoded output pins are
active low. The REV input on pin 13 (input B) is connected to a tactile
switch or collision avoidance IR and when active high, selects pin 9 and and
10 decoded outputs which drive the h-bridge inputs in reverse order and
causes the walker to back up.
In the attached schematic I have also shown the final version of the Power
Smart h-bridge which ensures optimum base drive for the motor driver output
transistors. The output transistors should be PN2222/PN2907 pairs or similar
for motor currents over 100mA.
The circuit has been extensively tested on a biobug platform with the
original biobug motors and it greatly reduces the motor current while
maintaining biobug speed and reverses flawlessly.
From: César Blum Silveira
To: BEAM Mailing List
Sent: 2/10/02 7:10 PM
Subject: [beam] Z-Bridge
I was taking a look at AA Van Zoelen's Z-Bridge and I have some